Large power amplifiers used in electronic devices, such as those capable of generating 100 watts of output power, are often constructed using high capacity discrete elements. An essential element is the power transistor which is used to convert an incoming signal to an amplified output signal. Because of the inherent inefficiencies of this operation, the power transistor generates large quantities of heat. This heat must be dissipated to prevent damage to the power transistor, to the surrounding electrical components, and to the electrical circuitry in general.
To ensure proper operation of the electrical circuitry, some components, such as the power transistor, must be compensated for impedance. For example, the electrical circuitry of a power amplifier may include impedance compensating circuit members, such as capacitors in close proximity to the power transistors. Location of the capacitors may be critical for the correct operation of the circuitry. In radio frequency (RF) applications, the benefits of correctly placed capacitors include maximization of RF output power and minimization of the heat dissipation requirements. Since variation of the location of these capacitors may significantly alter the characteristics of the circuitry, consistency in their placement is critical during the manufacturing process.
Large capacity power transistors are often available in packages which include a heat dissipation member, or heat spreader, and leads which provide electrical connection for input and output signals. Electrical grounding is also essential and thus leads for electrical ground connections are also included. A major problem with the current power transistor packages is the difficulty of accurately and consistently locating the capacitors for impedance compensation purposes. Usually, the arrangement of leads on such packages does not facilitate manufacturing when there is a design requirement to locate these capacitors as close as possible to the input and output leads of the power transistor device. Additionally, establishing and maintaining a thermal path from the heat spreader to other heat dissipation structures further complicates an assembly process which utilizes these devices.
Furthermore, to increase quality and reliability in the manufacturing process, and to further reduce manufacturing costs, it was long desired in the art to have these discrete elements packaged to facilitate their handling by automated part placement equipment. Thus, an improve package design is required to address the above-mentioned problems.